If you had sex 13days after end of period then probably you had sex on the 19th or 20th day of your cycle. Chances of pregnancy are less in this case. If you had intercourse on 13th day counted from the first day of your period then chances of pregnancy are more as ovulation usually occurs between 12-17th day, depending on your cycle duration.
To increase your chances of conceiving you must try multiple times close to your ovulation date.
How to know you have ovulated: Count back 14 days from the next expected due date of period, this gives the approximate date of ovulation in the present cycle. Some women get a spotting with ovulation and others get cramps. Almost everyone experiences an increase in white discharge around ovulation. There is always a rise in the basal body temperature (taken first thing in the morning before getting out of bed) around ovulation. There are ovulation tests available in market which you can use. Once you do this exercise for a month or two, you can know the fertile period well and should try during this time—3-4 days before to two three days after ovulation (detected through ovulation detection kit).
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.
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